INTRODUCTION: The use of sodium bicarbonate (NaHCO3) supplementation to improve repeated high intensity performance is recommended, however most swimming performance studies examine time trial efforts rather than repeated swims indicative of training sessions. The aim of this study therefore was to investigate the effects of sodium bicarbonate supplementation on sprint interval swimming reflective of a typical training session. METHODS: Fourteen trained competitive swimmers (body mass: 73±8 kg) volunteered for this double blind, randomised, crossover designed study. Each participant was asked to swim 50 m (front crawl), from a competitive diving block, at their maximum effort and repeat this 8 times (Interspersed with a 50 m active recovery swim). Each exercise bout was run off a 5 min base, which left the participants with approximately 3 min passive recovery. After one familiarisation trial, this was repeated on two separate occasions whereby participants ingested either 0.3 g.kg-1 BM NaHCO3 or 0.05 g.kg-1 BM sodium chloride (placebo) 60 minutes prior to exercise. Time to complete each 50 m interval was recorded, along with blood measures for pH and bicarbonate (HCO3-) using a Radiometer (ABL9, Copenhagen, Denmark) and lactate (Lactate Pro 2, Arkray, Japan) at rest, at 60 min (post-supplementation), and post-exercise. Aggregated gastrointestinal (GI) discomfort was measured using Visual Analogue Scales (VAS) within a range of symptoms throughout each trial. Two-way repeated measures ANOVA were used to assess performance and blood measures and were conducted using a statistical software package (SPSS V28, IBM, Chicago, IL, USA). Hedges` g effect size (ES) was also calculated for pairwise comparisons between treatments and interpreted using Cohens D thresholds. RESULTS: Performance was improved by NaHCO3 ingestion prior to the interval swimming (p=0.005, P?2=0.301). Whilst there were no differences between sprints 1 to 4 (p>0.05), improvements were observed in sprint 5 (p=0.011; ES=0.26), 6 (p=0.014; ES=0.39), 7 (p=0.005; ES=0.6), and 8 (p=0.004; ES=0.79). Following NaHCO3 supplementation, pH was greater at 60 min (p<0.001; ES=3.23), whilst for HCO3- it was greater at 60 min (p<0.001; ES=3.23) and post-exercise (p=0.016; ES=0.53) compared to placebo. Lactate was greater following NaHCO3 supplementation post-exercise compared to placebo (17.6±4.9 vs. 14.7±3.8 mmol.l-1; p < 0.001; ES = 0.64). Aggregated GI discomfort was higher for NaHCO3 compared to placebo (21±12 vs. 3±1; p=0.021; ES=2.05). CONCLUSION: These findings suggest NaHCO3 supplementation can improve the latter stages of sprint interval swimming performance, which is likely due to the augmentation of pH and HCO3- prior to exercise and the subsequent increase in buffering capacity. Performance improvements may be beneficial during high intensity training blocks in improving adaptation (via increasing exercise intensity training volume), however further research is warranted to investigate NaHCO3 and training responses.
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